The invention relates to ink jet printers and, more particularly, to a thermal ink jet printhead having a filter over its ink inlet and a laser ablation fabrication process for forming the filter.
A typical thermally actuated drop-on-demand ink jet printing system uses thermal energy pulses to produce vapor bubbles in an ink-filled channel that expels droplets from the channel orifices of the printing system's printhead. Such printheads have one or more ink-filled channels communicating at one end with a relatively small ink supply chamber (or reservoir) and having an orifice at the opposite end, also referred to as the nozzle. A thermal energy generator, usually a resistor, is located within the channels near the nozzle at a predetermined distance upstream therefrom. The resistors are individually addressed with a current pulse to momentarily vaporize the ink and form a bubble which expels an ink droplet. A meniscus is formed at each nozzle under a slight negative pressure to prevent ink from weeping therefrom.
Some of these thermal ink jet printheads are formed by mating two silicon substrates. One substrate contains an array of heater elements and associated electronics (and is thus referred to as a heater plate), while the second substrate is a fluid directing portion containing a plurality of nozzle-defining channels and an ink inlet for providing ink from a source to the channels (thus, this substrate is referred to as a channel plate). The channel plate is typically fabricated by orientation dependent etching methods.
Droplet directionality of a droplet expelled from these printheads can be significantly influenced by extrinsic particles finding their way into the printhead channels.
The dimensions of ink inlets to the die modules, or substrates, are much larger than the ink channels; hence, it is desirable to provide a filtering mechanism for filtering the ink at some point along the ink flow path from the ink manifold or manifold source to the ink channel. Any filtering technique should also minimize air entrapment in the ink flow path.
Various techniques are disclosed in the prior art. U.S. Pat. Nos. 5,124,717, 5,141,596, 5,154,815, and 5,204,690 disclose fabrication techniques for forming filters integral to the printhead using patterned etch resistant masks. This technique has the disadvantage of flow restriction due to the proximity to single channels and poor yields due to defects near single channels.
U.S. Pat. No. 4,864,329 to Kneezel et al. discloses a thermal ink jet printhead having a flat filter placed over the inlet thereof by a fabrication process which laminates a wafer size filter to the aligned and bonded wafers containing a plurality of printheads. The individual printheads are obtained by a sectioning operation, which cuts through the two or more bonded wafers and the filter. The filter may be a woven mesh screen or preferably a nickel electroformed screen with predetermined pore size. Since the filter covers one entire side of the printhead, a relatively large contact area prevents delamination and enables convenient leak-free sealing. Electroformed screen filters having pore size which is small enough to filter out particles of interest result in filters which are very thin and subject to breakage during handling or wash steps. Also, the preferred nickel embodiment is not compatible with certain inks resulting in filter corrosion. Finally, the choice of materials is limited when using this technique. Woven mesh screens are difficult to seal reliably against both the silicon ink inlet and the corresponding opening in the ink manifold. Further, plating with metals such as gold to protect against corrosion is costly.